Contact lenses have been used commercially to improve vision since the 1950s. Most current contact lenses are made of hydrogels formed by polymerizing hydrophilic monomers such as HEMA and vinylpyrrolidone in the presence of a minor amount of a crosslinking agent. The polymerization of the monomers results in shrinkage which may be as much as 20% by volume.
Prepolymers having backbones of PVA and reactive groups of acrylic groups have been disclosed. The reactive prepolymer is dissolved in water, and crosslinked inside a mold by irradiation with UV light to form a contact lens. The shrinkage during cure is small, but the hydrogels thus produced exhibits mechanical properties that may prove marginal for contact lens use.
U.S. Pat. Nos. 4,495,313, 4,889,664 and 5,039,459 disclose the formation of conventional hydrogels.